It is well known that natural waters and those found in underground formations contain hardness scale forming ions such as calcium which tend to precipitate and form deposits or scale. Thus, when such waters are used as cooling waters in cooling towers in many industrial processes there is a tendency for scale to be deposited and eventually it is necessary to remove such scale which in turn makes it necessary to discontinue operation of the particular process for a period of time until the scale can be removed.
The formation of insoluble calcium salts is also a problem in the secondary recovery of oil from subterranean formations by processes in which water is introduced into injection wells and forced through the underground formations to cause oil to be produced in a producing well. This type of process is usually referred to as a waterflood system.
In processes of the foregoing type where it is desired to prevent hardness scale deposits on metal surfaces or other surfaces in contact with hard water containing hardness scale forming ions such as calcium, it has been customary heretofore to add various types of scale inhibiting compounds including inorganic polyphosphates, organic phosphates, organic phosphonates, and some types of polyacrylates. These compounds have varying degrees of effectiveness and some of them are quite effective as scale inhibitors for the prevention of scale deposits in underground formations. Many of them, however, are not effective at a pH as high as 10 or under elevated temperature conditions. This is due to the fact that the compounds themselves are not stable against precipitation in waters containing as much as 5,000 mg/l calcium, calculated as calcium carbonate, at a pH of 10 and at temperatures of 160.degree. F or higher. Obviously, if the scale inhibiting compound itself precipitates from solution it will form a deposit which adds to the scale problem and in the case of waterflooding, water cooling or other processes where hard waters containing calcium are used, the compound will no longer be present in amounts sufficient to perform the desired function of inhibiting scale formation.